Russell Foster: Why do we sleep? | Video on TED.com http://www.ted.com/talks/russellfosterwhydowesleep.html?utmsource=newsletterweekly2013-08-24&utmcampaign=newsletterweekly&utmmedium=email&utmcontent=toprightimage Russell Foster is a circadian neuroscientist: He studies the sleep cycles of the brain. And he asks: What do we know about sleep? Not a lot, it turns out, for something we do with one-third of our lives. In this talk, Foster shares three popular theories about why we sleep, busts some myths about how much sleep we need at different ages -- and hints at some bold new uses of sleep as a predictor of mental health.